TDS (Total Dissolved Solids)

Concentration of dissolved solids in extracted coffee, measured in % or ppm by refractometer. SCA Gold Cup window: 1.15-1.35% (filter). Used with EY to diagnose extraction quality.

Background & Context

Total Dissolved Solids (TDS), measured as a percentage, is the mass of coffee compounds dissolved in the brew liquid relative to the total liquid mass. It is the precise scientific measurement of what coffee people call 'strength' — how concentrated or dilute a cup is. A refractometer, which measures how light refracts through the liquid (coffee dissolved compounds change the refractive index), is the standard tool for TDS measurement. The SCA target range for ideal filter coffee is TDS 1.15–1.35% (the 'Golden Cup' zone of the Brewing Control Chart). Espresso typically measures 8–12% TDS. Cold brew concentrate measures 3–6% TDS. TDS is frequently confused with extraction yield: TDS measures strength (how many dissolved compounds are in the cup relative to water), while EY measures efficiency (what percentage of the total available coffee solids were dissolved). The same coffee can be strong and under-extracted (high TDS from a high dose, but short contact time) or weak and over-extracted (low TDS from a low dose, but very long contact time). Both variables must be measured together on the Brewing Control Chart to make sense. TDS fluctuates with water temperature during measurement — refractometers must be zeroed with room-temperature distilled water and used at consistent temperatures for reliable readings.

Practical Use

For home baristas considering a refractometer: the VST Refractometer and Atago PAL-COFFEE are the specialty standards ($150–300). Even without a refractometer, you can intuitively track TDS: a 1:15 ratio brew with 20% EY is approximately 1.33% TDS — within the SCA target. If you want a stronger cup (higher TDS), reduce the ratio to 1:13 or 1:14 while keeping extraction consistent. For espresso: measuring TDS and comparing to yield weight gives EY directly: EY = TDS × (yield weight / dose weight).

Related Terms

Related terms: Extraction yield — EY and TDS together determine cup quality position on the Brewing Control Chart. Brewing Control Chart — TDS is one axis. Brew ratio — the main control variable for TDS. Body — body and TDS are related but not identical.